Plural camera television transmitter with electronic wipeout control



Oct. 7, 1952 E. D. HILBURN RLURAL CAMERA TELEVISION TRANSMITTER WITHELECTRONIC WIRE OUT CONTROL 2 SHEETS-SHEET l Filed April 8, 1949 HILBURNPLURAL CAMERA TELEVISION TRANSMITTER Oct. 7, 1952 2,613,263

' WITH ELECTRONIC WIFE OUT CONTROL 2 SHEETS-SHEET 2 Filed April 8, 1949Patented Oct. 7, 1952 PLURAL CAMERA TELEVISION TRANS, MITTER WITHELECTRONIC WIPEOUT CONTROL Earl D. Hilburn, Silver Spring, Md.

AApplicationApril 8, 1949, vSerial No. 86,273

The present invention relates generally to `tele-- vision picturetransmission's'ystems, and more particularly to apparatus and'm'ethodsfor`varying the composition of transmitted pictures, and for providingnovel video effects in accomplishing transition from one scene toanother. y

In the transmission of pictures "by means of television techniques, itis not generally `desirable to effect transition'irom one scenetoanother in a radical and sudden manner. Techniques have,accordingly,been developed for producing transitions gradually, and 'invarious novel and pleasing ways, many of whichhave beenadap'ted frommotion picture technique.

Various types of vtrarisitionsof scenes,jin the moving picture art, havelreceived names, as for example, fade-out, 'fade-in, wipe-out, lapdissolve, iris eiect, and the like.

A fade-out is the gradual disappearance of 1a picture from the screen`by reduction of 'its luminous intensity, the terminal result being acompletely dark screen. v

A fade-in is the gradual appearanceoi apicture on the screenbyincreasingits luminous intensity from zero to. full or normalbrilliance. A fadein is, therefore, the reverse of a lfade-out.

A dissolve is a vfade-out followed immediately by a fade-in of a new anddiilerent pictureon the screen.

When a fade-out and fade-in do lnot occur separately, or do not Jfollow`each other in time, but occur substantially at the same time so thatthe rst picture gradually blends 4into and becomes the second picture,such a "change "is commonly called a lap dissolve.

A wipe-out is 4the passing across "the screen oran outline or contour ofany desired shape and L'velocity of motion, voutside "of which onepicture exists, and inside of which a second-picture exists. The termsinside and outside in the lpreceding statement maybe replaced`byfrightffand left or above and below, orby any-combination of one ormore directions.

If one of the pictures is initiated'as 1a 4spot on the screen whichexpands in area, replacing the other picture, until the 1'flrst'pi'cture4occupies the entire screen, the eiiect is often dcalled an iris effect.Alternatively, an imagemay occupy, originally, the entire iscreen, ianda-nay "be compressed in area gradually. revealing, -as it compresses,the other 'image outside itself.- l

It vis the purposeof the `present Vinventi'onfto provide novelcircuits'and `methods 'for electrically producing wipe-outs and irisJeects inl the V-television art.

It is a further object of the-presentinverinnn to, provide the wipe-outand iris 'effects solely by means of electrical controls.

It is another obj ect .of the invention to produce wipe-outs intelevisionpicturetransmissionsin d claims. (ci. 17e- 7.2)

response to blanking Waves applied to the blanking controls oftelevision cameras. Y It is' -sti-ll another object of the invention `toprovide a novel system for'generating controlled gating wavesfor'application to television cameras, or for general application in theelectronic arts.

The above and still furtherwobjects and .advantages vof the inventionwill become yapparent upon consideration of the following detaileddescription-of aspecic embodiment therecnespef 'cially when taken inconjunction with `the accompanying drawings, wherein:

Figure 1 is a schematic circuit diagram of van embodiment of the presentinvention;

`Figure 2 is a diagram of a mask .used inthe system of Figure 1 forproducing 4iris eiect;

Figure 3 is a wave form diagram pertaining to the system of Figure 1;and

Figures 4, 5 and 6 illustrate further masks utilizable-inthe system ofFigure'l. y

It will be realized that inthe television art, fade-ins and fade-outsand l-ap dissolves may .be accomplished very readily by utilization ofvol'- ume controls supplied for controlling the outputs of televisioncameras. The problem of .producing wipe-outs and iris effects, and thelike, however, is a more complex problem involving the timing of theoperation of two television cameras. Various solutions to the problem of.producing `wipeouts and iris effects have been advanced. "For example,solutions are providedzin U. yS.,Pat, ent #2,164,297 'issued to A. V.Bedford on June 2'7., 1939, 'in U. S. Patent #2,172,936 issued to A. N.Goldsmith on September 12, 1939, andthe U. S. patent to A. N.Goldsmith#2,193,869 iissued .on March 19, 1940. i'

Briefly described,. in accordancewith the present invention, wipe-'outand iris effects are .pro- Aducedfby means of flying spot technique,vthelrlying spot 'being produced by a cathode ray .tube

in terms of a pattern onthe face .thereof `which duplicates ands'synchronized with the scanning pattern applied to the cameras. Lightenergy from the flying-spot is translated into electrical `gating waves,which are then applied tothe blank- The` cameras :may vbearranged to vbenormally on, that is, tobe lnor,- mally producing picture signalsand are.provided with blanking means in the iormr ci cathode ray beam controlelectrode to which may lbe applied negative voltages for blanking `outthebeampand --accordingly, orpreventing generation of :picture signals.In the usual operation of suchfcamera's blanklng out occurs while thecathode ray ,beam ofthe cameras are retracingpreparatory'toscanningsuccessive linesof thepicture, and, further, Awhilethe cathode ray beamsare retracing jpreparatory to rescanning acomp-lete jfrarne cf--thepicture. In accordance with the presentj'invention, the gating waves,derivingjrom the flying 'amazes and the photocell for determining thetimes dur- Y Y ing which light from thej flying spot reaches thephotocell, and, accordingly, the times when the gating wave is on andwhen it is 91T, Circuits 'are further provided for shifting the entireflying spot pattern, vertically, horizontally, or in a combination ofthese directions, and further for varying the size of the yingspot`pattern at will. yAccordingly, the mask may be retained in a singlefixed position and the ying spot pattern shifted with respect to themask to vary the character of the gating wave. Thereby extremeflexibility of operation is attained, to accomplish wide variety ofwipes and iris effects, by providing various combinations of motion ofthe flying spot scanning pattern with variations of size of the pattern.It is, accordingly, still a further object ofthe present invention toproduce wipe-out and iris effects in'television picture transmission inresponse to blanking waves generated by a flying spot in a cathode raytube, the spot following a scan pattern which is normalin televisiontechnique, and synchronized with the similar scan pattern provided atthe television cameras, the flying spot pattern being movable in anydirection and being variablev as to size, with respect to'a stationarymask.,Y y l Referring now more specifically to the drawings, thereference numerals I and 2 identify orthicon or'iconoscope cameras #Iand #2, respectively, which, during avtelevision transmission mayexamine different scenes, or different aspects of the same scene. VAlead 3 4applies to the camera I the usual blanking pulses, while asimilar lead 4 applies'blankingl pulses to the camera 2. It will beunderstood then,that both cameras I and 2 normally generate picturesignals, s0 long as no gating wave is applied thereto over the blankingleads 3 and 4, and in the absence of the normal blanking pulses. i

Connected to the leads 3 and 4, respectively, are

switch arms 5 and 6, which are shown ganged by means of a linkage 1, butwhich may, if desired, be left unganged to provide greater flexibilityof operation. The switch arm 5 is comprisedl in a switch 8 having threecontacts 9, I I and II, with which the switch arm 5 may be selectivelyplaced in contact. Similarly the switch arm 6 is part of a switch I2having three contacts I3, I4 and I5, with which the switch arm 6 may beselectively placed in contact. l

'A source of blanking pulses may be provided, which is not illustrated,but which provides blanking pulses to a lead I6. These blanking pulsesare applied from the leadV IG-to the contact 9 of the switch 8 and tothe contact I3 of the switch I2. Accordingly, when the switch arms 5vand 6 are in contact with contacts Sand I3, respectively, the cameras Iand 2 are provided with normal blanking pulses, which blank out thecathode ray beams of the cameras I and 2 between lines and betweenframes.

Cameras I and 2 may, further, be operated'in synchronlsm with suitablesignal sources comprised'in a sync signal generator I1, horizontaldriving pulses being applied via the leads I8 and I9 in parallel to bothcameras i and 2, and vertical driving pulses being applied via the leads20 and 2I in parallel to both cameras l and 2.

' The operation of the cameras I and 2 in response to the drivingpulsesprovided over the leads I9 and 2|, and in response to the blankingpulses provided over the lead I6, is conventional and well understoodand need not be described in detail in this specification.

A flying spot generator is provided, in the form of a cathode ray tube22 and associated cathode ray beam scanning signal sources. The cathoderay tube 22 is provided with the normal complement of control and beamgenerating electrodes, and may in fact be a relatively conventionalcathode ray tube having, however, an extremely fast or short persistencescreen. More specifically, the cathode ray tube 22 may be provided witha blanking or beam intensity control electrode 24, and with verticaldeflection electrodes 25 and horizontal deflection electrodes 26. Theblanking electrode or beam intensity control electrode 24 is coupled viaa blanking. signal amplifier 21 to the lead I6, and, accordingly,cathode ray tube 22 is blanked whenever cameras I and 2 are blanked.,lScanning voltages for the cathode ray tube 22 are supplied via a,horizontal saw-tooth generator 28, 'which is synchronized from the leadI8, and via a scanning voltage amplifier 20. Vertical scanning voltagesare supplied to the cathode ray tube in the form of sawtooth signalsprovided by a vertical saw-tooth generator 30, the output of which isamplified in a vertical saw-tooth wave form amplifier 3|, the verticalsaw-tooth generator 3D being synchro nized via the lead'2Il.Accordingly, the scan taking place in the cathode ray tube 22 isprecisely synchronized with that taking place in the cameras I and 2.The'pattern 32 traced on the face 23 of the cathode ray tube 22duplicates that traced by the scanning beams of the cameras I and 2,taking the usual form of a series of successively vertically displacedsubstantially horizontal lines. While the above description, andstructure illustrated in the drawings, involve a cathode ray tube havingelectrostatic deflection electrodes, obviously electro-magneticdeflection may be employed without departing from the true spirit of theinvention.

A photocelll 33 is provided with its cathode facing scanning pattern 32.A suitable lens 34 may be interposed between the pattern 32 and thephotocell 33, to concentrate light from the pattern 32 in the photocell33. A mask 35 may be interposed between the pattern 32 and the lens 34.Accordingly, light from the pattern 32 vreaches the photocell33 andenergizes the latter whenever a line joining each instantaneouscomponent of the trace 32 with the photocell 33 is not blocked by themask 35. y

The output of the photocell 33 is amplified and clipped in a videoamplifier and clipper 36, and, the output of the amplifier and clipper36 is applied over a lead 31 directly to the contact Ic of the switch 8,and via a lead 38 to one stage 39 a mixing and phase reversingamplifier, the output of which is applied via a lead40 to the contact IIof the switch 8, and to the contact I4 of the switch I2.

The output of the video amplifier 36 con-` stitutes a negative gatingpulse, which, when applied to the camera-I over the'lead 31 and viaamazes the contact lIll oi the lswitch-arm y15,-s'huts o'nlthescanning'beam of they cam-era Tl. rIhis negative gating pulse, afterpassing through the Vmixing amplier 39', is of reverse' phase, sothatthe positive portions thereof, asat 38,1become negative gating pulses,which arelapplied tothe contact Il of the switch 8 and to thecontact l4othe switch l2. v

The negative gatingV pulses supplied by the video amplier 3B are further`applied. vvia the lead 31 to the switch contact I5 lofftheswitch l2,and the output of the mixing amplifer'39' is applied to the switchcontact 5H of -theswitch 3. Accordingly, when the switch 'arms 4v5 and 6contact the switch contacts 'l0 and I4, "respectively, the negativeportions of the gating wave supplied by the video ampliiier T36 4serveto cut off the camera I while the positive portions-38 thereof serve tolout oit the camera 2. On the other hand, when the switch `arms 5 and 8are in contact with switch =contacts |"I land. l5, the negativeportionsof thegating wave serve 'to lcut off the camera 2 while thepositive'portionl serves to cut off the camera l. While the switch arms5 and 6 are in contact withswitchcontacts -9 and I3, on the other hand,the gating waves supplied by the video amplifier 3B havejno effect oneither of cameras l and 2, but thenorma'l blanking pulses supplied Iover"the lead I6. are applied in paralleltothe cameras l and 2 'andthe-cameras l and 2 'operate in' the normal and usual fashion for suchcameras. When vthe switch arms 5 and 6 are on contact l0, `Il or I4, I5,on the other hand, the cameras Ifand *2 are blanked in alternation, thatis, vone is blanked while the other isl unblanked and the 'camera whichis blanked and that which is unblanked in response to desiredl portionsof Vgating lwaves may be selected by properly 'positioning the switcharms 5 and 6.

The horizontal saw-tooth'generator 28 may be provided at its output withapotentiometer 40 to enable application to the'input of the horizontalsaw-tooth amplier 29 of a saw-tooth voltage of any desired magnitude.The magnitude ofthe saw-'tooth voltage as applied tothe horizontalamplifier 2S in turn determines the Vhorizontal dimension of the pattern32. By adjusting 'the output of the horizontal sawtooth generator 28bymeans of the potentiometer 40 to have zero amplitude, the pattern 32may degenerate finto a single vertical line, while by utilizing 'thefulloutput of the horizontal saw-toothpgenerator 28 the pattern maybe causedto occupysubstantially the entire face of the cathoderay tube22.

A similar potentiometer 4l provided in conjunction with the outputcircuit 4of the vertical saw-tooth generator 30, for the same purpose,enables adjustment of the vertical vdimension of the pattern 32. Thepattern 32, accordingly, may be arranged to have any aspect ratiodesired, .and not only the normal 4 to 3 aspect .ratio utilized inconventional television systems. The pattern may, further, be arrangedto have Aany desired vertical and horizontal dimensions, which areindependently adjustable.

Atthe output of the horizontal amplier'ZS is provided a conventionalmixing .circuit 42 comprising a positive terminal 43 and a negativeterminal 44, a resistance 45 `being connected between the positiveterminal 43 and the negative terminal 44 and fa, similar resistance 46betweenthe negative terminal 44 and the positive ter minal 43. Theoutput -of the horizontal-amplifier iii` is appliedto the resistor4'5'overavafriable'ltap negative. 48 mid-way of the resistors 45 and:46, on the .tionEiZ surrounding the central `pattern 5l.

"parent portion 52 of the -mask'td "becomes longer.

6 412, and the horizontal Vdeflection electrodes 2S vconnected via'variable tap 43 to any selected position in resistor 46.

'The fulloutputof the horizontal amplifier 29 is applied to thehorizontal deflection electrodes 26 regardless `of thepositionof the`contacts 4l' yand 43` because ythese horizontal deection electrodes "26are, at all times, connected directly to the output leads from thehorizontal amplifier 29. Onfthe other hand. one vof the deectionelectrodes 26 is connected to 'the lvariable tap 41 while the other isVconnected to the variable tap S48, and, accordingly'by varying thevariable taps 41 vand "48 in respect to theirl'vpositions along theresistorsr 45 and 4B, the D.C`. potentials applied tothe deiiectionelectrodes 25 may be varied over a range of values, and reversed andthereafter again varied over a range of `values in reverse sense.

'For example, with the `contacts 4l' and 48 in their lowermostposition', one oi the Vdeiiection electrodes 12E is positive andtheother negative,

yinaccordance with the total D.C. voltage availotherofthe deflectionelectrodes 25 becomes positive while the previously positive one becomesFora position of the contacts 41 and other hand, `potential on both`deiiection electrodes 26 is identical. Accordingly, the positions ofthe contacts 41 and 48 determine rthe center position vof the beam ofvthe cathode raytube 22, or the vposition in the absence Vo'f.fsaw-toothdeflection voltage, and, accordingly, determine .the median position ofthepatterntZ horizontally ofthe face of the indicator 22. A similarcircuit 5d islprovided for .centering the pattern .32 vvertically ofAthe face 23 of the cathode ray 'tube122.

Considering now the `operation of the present :system in producing aniris elicot, a mask 35 is utilized, which `has a, circularl opaqueportion 5i (see Fig. 2), and which has a transparent por- Assume now'that the niaskitd is interposed between the ipattern'32 andthephotocell 33, and that the total extent of scanboth vertical andhorizontal is substantially superimposed on the outline of the mask atthe limits .of the transparent yportion thereof. Referring morespecically to Figure 3 of the drawings they-relative position of normalblanking pulses provided over the line l5 are illustrated. Theseblan'hing pulses occur at the same position for various verticalpositions of Athescann'ing pattern, as for example, along line line -yand line e. For the-line rhowever, light reaches the photocell 33 onlywhile the beam of the cathode ray tube 22 is traversing the trans-Accordingly, we `see at 'line B of Figure negative pulse 53a which iscaused by passager-'o the cathode ray beam across the central pattern onthe level of the line x. Passing to the liner, the central pattern'iswider and thegating wave- 53?) accordingly At the line s the total scanduru ing which lightpasses to the;photocell 33 is at its minimumv sincethe line Va-is drawn 'diametrin "cally across the central patternf'-l,and, accordingly, the scanning wave 53e has attained a maxi wave 153ecorrespond in relative length to the *transparent{portionlof'the'maskf35 at the line e.

@The =wave 'forms shownat line-'B lof Figure 3 may be applied over theline 31 to camera number I, if the switch arm is in contact with theswitch contact Ill, and in such case this blanking wave is not appliedto camera number 2, but is applied zontal dimensions of the pattern 32and its position, then, the entire pattern may be caused to fallwithinthe transparent portion 5,8, or the pattern-4 mayl be expandedvIIC-rizontally until the to the mixing amplifier 39', which acts toreverse 5 majorportion thereofA falls on the opaque porthe phase of theblanking wave and to apply to the contact I 4 of switch I2, whichis nowconnected to camera number 2, a blanking wave of the characterillustrated in line C of Figure 3 of the drawings. It will be evidentthat the negative gating wave, shown in line B as applied to cameranumber I, will eliminate picture signal transmission during the timethat the gating wave is more negative than the zero axis, and willpermit generation of signal pictures at all other times. Similarly, thegating wave applied to camera 2 will disable picture transmission whilethe gating wave shown in line C is negative with respect to the zeroaxis, and will permit picture signal transmissions at all other times.It will be clear from the diagram that the times of picture signaltransmission are complementary, that is, that one camera is on while theother camera is off during each line of scan.

Accordingly, cameras I and 2 transmit in alternation during eachhorizontal trace of the cathode ray beams thereof, the rst cameratransmitting while the beam of the cathode ray beam 22 is aligned withthe transparent portion 52 of the mask 35, and the second cameratransmitting while the cathode ray tube 22 is aligned with a centralpattern 5I of the mask 35.

The size of the pattern 32 may be reduced by controlling thepotentiometers 40 and 4I. If the entire scan pattern 32 is aligned withthe central pattern 5I of the mask only the camera 2 will transmit, thecamera I being completely inactive. As the potentiometers 40 and 4I arevaried inrespect to position, the pattern 32 may be gradually expandedin size so that eventually substantially the entire pattern is alignedwith the transparent portions of the mask 35, the central pattern 5Icorresponding with a substantially small portion of the scan pattern 32.When this condition has been reached, thel camera I will be transmittingsubstantially all time, and the camera 2 will be substantially inactive.Transmission may thereby be transferred from one camera to the other interms of an iris effect.

Similarly for wipe-outs, a mask may be provided which covers a portionof the pattern 32 for one size and position thereof. If we assume thathalf the pattern is covered along a vertical line thereof, for example,cameras I and 2 will transmit in alternation along each horizontal lineof scan, if the mask covers a portion of the pattern 32. Variation ofthe transmission times as between cameras I and 2 may be accomplishedreadily by varying the position of the pattern 32 horizontally,vertically, or simultaneously horizontally or vertically, as desired, bycontrolling the centering circuits 42 and 50, or alternately bycontrolling size of the pattern 32 by means of the controls 40 and 4I.

To provide a specific example, I may use a mask as illustrated in Figure4 of the drawings, having a rectangular transparent portion 55 and twoopaque portions 56, which bound two vertical edges of the transparentportions 55. Horizontal scan may take place over a range correspondingwith the line 51. Accordingly, one camera will be on during the timecorresponding with scan over the line 58, while the other camera will beon for times corresponding with the line length and position of the-line59. By varying the -horl-f tion of ,the mask, providing an extremelynovel wipe-out. The ratejat which the wipe-out may be caused to occursimilarly may be readily ccntrolled in terms of thev rate of variationof the centering circuits 42, or of the amplitudes of the sawtoothscanning voltage as controlled by the potentiometerv 40. A

A furtherv novel type of wipe-out may be generated by means of a mask ofthe character illustratedin Figure 5 of the drawings, wherein an Lshaped -mask is' provided. The scan may be caused to occupy thetransparent portion of the mask 6l), as at '5I. The pattern 6I may begradually fed to the right until it is partially masked by the L-shapedportion 62 and then gradually reduced in width untilit is completelymasked by the opaque portion 62l of the mask 60. Alternatively, thepatterns] may be fed vertically until it is hiddenA by'the horizontalleg 63 of the mask 60, being first shifted vertically upward and thenmade smaller in size, to this end.

.As a rfurther modification, illustrated in Figure 6 of the drawings,the pattern 6I may be fed simultaneously vertically and horizontally,and reduced in size, until eventually it is behind the opaque portion atthe corner 64 of the pattern 60.

Obviously, any combination of the motions described-may be utilized', toprovide a practically inexhaustible variety of wipe-outs.

Considering again the iris effect mask which is illustrated in 'Figure2y ofthe drawings, it will vbe clear. that modified iris effects may beproduced by varying the aspect ratio of the pattern 32 prior toexpansion or contraction of the overall area of the pattern 32 toproduce the iris effect, and that so varying the aspect ratio of thepattern 32 has a similar effectvtol that which would be providedbyvarying the shape of the iris. In this manner, various elliptical ornon-circular iris effects may be produced. Still further iris eifectsmay be accomplished by utilizing square shaped, diamond shaped, key holeshaped, apertures, and thelike. f

'It is of importance to note that the present systememploys fixed masks,and a moving scanning patte'rn which is movable either vertically orhorizontally, orl both vertically and horizontally simultaneously, andis variable in respect to overall area. This possesses the advantage ofgreatly simplifying the mechanical and optical features of systems ofthe character disclosed for producing novel effects. y

` No 'complications will be encountered due to changing screenbrightness, in the present systen 1,jas the size of the scan patternvaries, since I provide in the amplifier 36 a clipping circuit orlimiting circuit, which assures that thel output wave forms are ofuniformamplitude for all conditions and adjustments of the pattern 32.Further, defocusingvy and spot size changes associated with variationsby size of the pattern 32 are of no practical importance, sinceimperfectly defined edges between two scenes on the same screen may betolerated while they are in process of change, or for short periods oftime.

Further, control of special effects in television picture transmissionis obtained, by the present system, utilizing existing camera blankingsystem, and thereby minimizing transient effects f which would occurwere blanking to occur in the I11 2. The s'ystem of producing wipe-outeffects in television image signals which comprises, meansy'It'orindependently and separately 'scanning "a first object area, asecond object area, andla predetermined portion of a control area, insynchro- 'vnism,`to produce from e'ach scanning a series of signals,means for utilizing thesignals deriving from said predetermined portionof said control varea to suppress selectively and valternately thesignals deriving fromthe object areas, and means for continuouslyvaryingthe size andthe dimensions of said predetermined portion of saidcontrol area by selectively varying a plurality of control voltages.

`3.` 'A picturev transmitting system comprising liirst means forproducing electrical signals representativev of a first scene, saidfirst means comprising a first television-camera having a rstpicturefscanning cathode ray tube, said cathode 'ray tube having afirstblanking control circuit including 1 :an intensity-controlelectrode, and

means for applying blanking waves to said blanking. control circuit,second means for producing -electrical signals representative of asecond scene,'said second'meanscomprising a secondtelevision'cam'erahaving a second picture scanvsynchronism to scan apicture area, means for generating rst'and second blanking waves insynchronism with said scanning, said last means comprising a flyinglight spot scanner having means for moving alight spot in synchronismwithsaid beams of electrons and in a predeterminedp-attern, and means'for varying the size and position of said pattern at will, said firstand second blanking waves occurring in time succession and having a sumof durations equal to and substantially coincident with each horizontalscan of said beams of electrons, means for applying one of said blankingwaves to one of said blanking control circuits and means for applyingthe other of said blanlring waves to the .other of said blanking controlcircuits.

4.- The combination in accordance with claim 3 wherein said means forgenerating said first and second blanking waves comprises means forgenerating a third beam of electrons, means for scanning said third beamof electrons horizontally and vertically to scan an area in synchronismwith said first mentioned scanning, a fluorescent surface in the* pathof said third beam of electrons, whereby said scanning of said thirdbeam of electrons generates an illuminated pattern on saidviiuorescent-surface, a photoelectric cell positioned to receiveillumination from-said illuminated surface, and arranged to lgeneratesignals in response to said illumination, and means responsive tosaidsignals for generating said blanking waves.

5. The combination in accordance with claim 4 wherein is provided a maskhaving opaque and transparent portions, interposed between saidilluminated pattern and said photo-electric cell, and means for varyingthe position and the size of said illuminated pattern on saidfluorescent surface to vary the character of said gating Waves.

6. A systeml for producing novel .visual effects in television,comprising, a rst television camera for scanning a first object area,said television camera comprising a cathode ray tube having avblanlringgrid, a. second television camera for scanning a second objectarea in synchronism with said first object area, said second televisioncamera comprising a cathode ray tube having a blanking grid, means forgenerating a scanning raster for scanning a control area having twosub-areas of mutually diierent characteristics in synchronism withscanning of said rst andsecond object areas by said first and secondcameras, means responsive to said last means for generating blankingvoltage only when scanning one of said sub-areas, means for applyingsaid blanking voltage to one only of said blanking grids, means forvarying at will the location and size of scanning raster, wherein saidmeans for generating a scanning raster comprises a cathode ray tubehaving a fluorescent surface, means for generating an electron beam, andmeans for controllably directing said electron beam-against saidfluorescent surface in a pattern corresponding with said scanningraster.

7. A system for producing novel visual effects in television,comprising, a single source of synchronizing and negative blankingpulses, a rst television camera responsive to said synchronizing andblanking pulses for scanning an area, a second television cameraresponsive to said synchronizing and blanking pulses for scanning anarea, a cathode ray tube control device responsive to said"synchronising and blanking pulses for scanning a control area having atleast two sub-areas of selectively light responsive and non-responsivecharacteristics, and for producing gating waves in response to scanningsaid non-light responsive sub-area and in response to said blankingpulses, a rst and a second phase reversing and mixer amplier ccnnectedin cascade, means for applying said synchronizing and blanking pulses tosaid rst amplier, means for applying said gating Waves to said secondamplifier, means for selectively connecting said single source ofsynchronizing and negative blanking pulses directly to said rst andsecond television cameras, means for at will applyingI said gating wavesdirectly to one of said cameras and via said second amplifier to theother of said cameras, and means for applying said gating waves directlyto the other of said cameras and the output of said second amplier tosaid one camera, to effect selective blanking of`said cameras.

i EARL D. I-IILBURN.

REFERENCES CITED vThe following references are of record in the file ofthis patent:

UNITED STATES PATENTS

